<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box{
      font-size: 30px;
    }
    .wrap{
      font-size: 20px;
    }

    h2{
      font-size: 10px;
      width: 10em;
      height: 10em;
      background-color: aqua;
    }
  </style>
</head>
<body>
  <div class="box">
    <div class="wrap">
      <h2>hello world</h2>
    </div>
  </div>
</body>
</html>